1. Field of the Invention
The present invention relates to a liquid discharge head mounted in a recording device that carries out recording by discharging liquid, such as ink.
2. Description of the Related Art
A liquid-discharge type recording device, such as an inkjet printer, is a so-called no-impact recording device and carries out high-speed recording on various different recording media while generating almost no noise during recording. Thus, the recording device is used in a wide range of apparatuses, such as printers, word processors, facsimiles, and copiers.
Japanese Patent No. 4338202 describes an example of such a liquid discharge head. The liquid discharge head includes a recording element substrate, an electric wiring substrate, and an ink tank. The recording element substrate has an electric thermal conversion member, which is a thermal resistor. The ink is heated by the electric thermal conversion member and is discharged as ink droplets as a result of film boiling. Driving signals, etc. from the main body of the device are applied to the recording element substrate via the electric wiring substrate. The ink tank for supplying ink is disposed on the recording element substrate and includes a negative-pressure generating mechanism that retains the ink and generates negative pressure. The ink tank has a guide and a positional reference, which are used when installing the liquid discharge head on the main body of the device.
Such a liquid discharge head is produced, for example, in the following process. First, the ink tank is prepared by performing injection molding of thermoplastic resin. Then, a filter made of stainless fiber that filters unwanted substances in the ink is bonded to the ink tank. Next, the electric thermal conversion member, a discharge port group, and an ink supplying port are patterned on the recording element substrate. A liquid discharge head that discharges only one color of ink, such as black, includes an ink channel, a filter, an ink supplying port, and a discharge port group. A liquid discharge head that discharges two or more colors of ink includes ink channels, filters, ink supplying ports, and discharge port groups which correspond to the different colors of ink. Then, an electric connection pad of the recording element substrate is connected to inner leads of the electric wiring substrate.
Then, a first adhesive is applied to a surface of the ink tank where the recording element substrate is bonded, and the recording element substrate is bonded at a predetermined position. Similarly, a second adhesive is applied to a surface of the ink tank where the electric wiring substrate is bonded, and the electric wiring substrate is bonded at a predetermined position. Then, a first sealant is applied with a dispenser to the periphery of recording element substrate, is allowed to sufficiently flow, and fills the gap between the recording element substrate and the ink tank. Furthermore, a high-viscosity second sealant is applied to the electric connection pad of recording element substrate and the inner leads of the electric wiring substrate. Subsequently, the adhesives and the sealants are thermally cured at once. Then, porous resin that retains the ink and generates negative pressure is placed inside each ink tank; a predetermined amount of ink of each color is injected into the corresponding ink tank; and a covering member is joined to each ink tank. Among the liquid discharge heads produced in this way, only good-quality products that have passed various inspections are selected, packaged, and shipped.
If the four sides of the recording element substrate in a liquid discharge head are sealed with a sealant, the sealant holds down the recording element substrate. Therefore, the recording element substrate may be damaged infrequently by stress applied to the recording element substrate due to a temperature or humidity cycle.
As a solution to this, Japanese Patent Laid-Open No. 10-000776 discloses a technique for bonding a recording element unit to an ink tank after sealing an electric connecting part of the recording element unit with a sealant. With this technique, the four sides of the recording element substrate do not need to be sealed with a sealant, and only the electric connecting part is sealed with a sealant. Therefore, damage to the recording element substrate due to a temperature or humidity cycle is less likely to occur.
With the technique described in Japanese Patent Laid-Open No. 10-000776, a bonding failure, such as a pinhole, at the bonding part (adhesive) bonding the recording element unit to the ink tank may lead to a defective product because ink will may leak from the bonding part where the sealant is not applied.